Docs: Added README and contributing guide (#124)

Co-authored-by: Burer <burer@kolibrios.org>
Reviewed-on: KolibriOS/kolibrios#124
Reviewed-by: Burer <burer@kolibrios.org>
Reviewed-by: rgimad <rgimad@noreply.localhost>
Reviewed-by: Ivan B <dunkaist@noreply.localhost>
Reviewed-by: Sweetbread <risdeveau@codrs.ru>

CONTRIBUTING.md

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+# Contributing guide
+
+## Type of contributing
+
+There are two main types of contributions accepted to the main KolibriOS repository:
+
+- Submitting issues about problems in the project
+- Submitting code to the project via pull requests
+
+Both these types are described in detail below.
+
+## Issues
+
+You can help us by submitting issues about problems found in the system. Currently, there are two main ways of submitting an issue in the project: **Bug Reports** and **Feature Requests**:
+
+- Bug Reports are suitable if you find a **bug** (crash, error, unexpected behavior) in some part of the system (kernel, drivers, apps, etc.) and want to report it
+- Feature Requests are used, when you want to propose some **improvement** to the system (missing features, improved user experience, etc.)
+
+## Pull requests
+
+You can also help us by submitting code via pull requests. The process of submitting a pull request consists of the following steps:
+
+1. Find what you want to implement or improve
+2. Make a fork of kolibrios (or other needed) repository
+3. Create a branch with a name that matches your changes
+4. Implement and test the changes
+5. Create commits according to the [accepted style](#commit-style)
+6. Create and submit a pull request into `main` branch
+7. Wait for CI/CD pipelines and code review to pass
+
+When a pull request is submitted, at least two project participants must conduct a code review, after which the proposed changes need to be corrected (if requested) and merged into the project.
+
+## Commit style
+
+### Message pattern
+
+The commit message should look like this:
+
+```test
+Commit message header
+
+Commit message body, if needed
+```
+
+- Commit message header and body should reflect changes made in commit
+- Commit message body should be separated from the header by one empty line
+
+### Length
+
+Maximum number of characters in a commit header is **72** (standard for **Git**). Also, **72** is the maximum length of a line in a commit body.
+
+### Multiple authors
+
+If you are making a commit together with another developer, you need to add:
+
+```
+Co-authored-by: ANOTHER-NAME <ANOTHER-NAME@EXAMPLE.COM>
+```
+
+to the end commit message body on a new line.
+
+### Merge commits
+
+> [!WARNING]
+> Merge commits are **prohibited** in the project
+
+Use **rebase** to keep your branch up to date.
+
+## Conclusion
+
+We hope this small instructions will help you to get familiar with KolibriOS contribution rules and inspire you to participate in the life of our project.